Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for controlling output of a seismic source.
Discussion of the Background
Marine seismic data acquisition and processing generate a profile (image) of the geophysical structure (subsurface) under the seafloor. While this profile does not provide an accurate location for oil and gas reservoirs, it suggests, to those trained in the field, the presence or absence of reservoirs. Thus, providing a high-resolution subsurface image is an ongoing process for the exploration of natural resources, including, among others, oil and/or gas.
During a seismic gathering process, a seismic survey system 100, as shown in FIG. 1, includes a source S that generates seismic energy and a receiver R that records seismic data corresponding to the seismic energy. Seismic waves are typically emitted by source S in all directions, for example, a seismic wave 102 that propagates away from the earth surface 104, toward a geological structure 106, and a seismic wave 108 that propagates toward the earth's surface 104. Both seismic waves 102 and 108 are then recorded, after being reflected, at the receiver R. However, the first seismic wave 102 (the primary) contains information about geological structure 106, which is valuable information, while the second seismic wave 108 (the ghost) does not contain any information about interface 106.
In the context of land seismic monitoring, it is desirable to reduce or cancel the emitted source ghost (upgoing wave-field) 108 for the reasons discussed above, but also because this type of wave travels through the near-surface layer 110, which is known to have properties that vary in time (e.g., with temperature). The ghost wave-field also degrades a 3-dimensional (3D) or 4D signal used to characterize a reservoir.
The traditional approach for dealing with the ghost involves recording both wave-fields (primary and ghost) and during a post-processing phase, e.g., after the recorded seismic data is received and processed at a processing center, or during a post-processing phase in the field, to separate and reduce/remove (or back out) the ghost as well as possible. Such an approach is described, for example, in Leaney and Schlumberger, “Parametric Wavefield Decomposition and Applications,” 60th Ann. Internat. Mtg., SEG San Francisco, 1990 (herein Leaney). Another approach is described in R. Soubaras, “Deghosting by joint deconvolution of a migration and a mirror migration,” 80th Meeting, SEG Expanded Abstracts, p. 3406-3409, 2010, the entire content of which is incorporated herein by reference. The traditional approach has multiple disadvantages: the process of separating and reducing/removing the ghost is computer-intensive and is not obtained in real time. As the analyzed signals are processed with an incoherent phase, the signal to noise ratio of the deghosted result is reduced compared to the same process performed directly at emission.
Thus, there is a need to have another approach that removes or reduces the ghost earlier in the process, to have a better signal to noise ratio and directly record the deghosted signal without costly post-processing.